Here’s Why You Need to Disconnect the Negative Battery Terminal When Working on Your Car

Disconnecting the battery during repairs is a pretty standard procedure regardless of the type of issue you’re dealing with.

Along with this protocol, disconnecting the negative terminal first before the positive terminal is a must.

But what’s the reason behind this practice?

Why Disconnect the Car’s Negative Battery Terminal When Working on Repairs

The negative battery terminal, also known as the ground strap or cable, is directly connected to the vehicle’s engine, body, and chassis. The positive terminal is connected to the starter, the alternator, and the fuse boxes.

Removing the positive terminal without removing the negative terminal can create a situation where a tool that is touching the engine or body can still short out against the positive battery terminal. While this isn’t likely to happen, it’s still a good idea to remove the negative terminal, even if only one of the two terminals is being disconnected.

If you’re just going to remove one terminal, remove the negative terminal rather than the positive terminal.

Removing the positive battery terminal without removing the negative terminal can create a situation where a tool that is touching the engine or body can still short out against the positive battery terminal. While this isn’t likely to happen, it’s still a good idea to remove the negative terminal, even if only one of the two terminals is being disconnected.

If you’re just going to remove one terminal, remove the negative terminal rather than the positive terminal.

–Richard McCuistian, ASE Certified Master Automobile Technician

Here are other problems that can arise when you fail to disconnect the car battery’s negative terminal first:

• Damaged electrical components
• Physical injury
• Fire 

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: If you only disconnect the positive terminal, the entire engine and car body are still connected to the battery. If you disconnect only the negative terminal, the likelihood of an accidental short circuit is practically zero.

When to Disconnect a Car Battery

It’s best to disconnect your vehicle’s battery in the following situations:

• When you need to recharge or replace the battery
• When you’re conducting maintenance
• If you’re not going to use a vehicle for months

How to Disconnect a Car Battery

When disconnecting a car battery, it’s always important to make sure that the engine is turned off. Attempting to remove a battery while the engine is on can spike sensitive electronics and cause a lot of damage.

The next step is to locate the battery. Most vehicles have it under the hood, while some have it under the trunk. Always consult your owner’s manual to determine the right location.

The next step is to locate the battery terminals. The negative terminal is usually denoted by a “-” symbol, while the positive terminal has a “+” symbol. In most cases, the positive terminal also comes with a red plastic cover.

A black battery cable connects to the negative terminal, while a red cable connects to the red positive terminal, signifying its hazardous nature.

Using a wrench, loosen the nut on the negative terminal and take it off the battery post. Make sure that the cable isn’t anywhere near the terminals. Then, proceed with removing the nut on the positive terminal.

Charging the Battery the Right Way

Dead batteries aren’t always a lost cause. In some cases, you only need to recharge them to get them up and running. Here’s the right way to charge your car’s battery.

Step 1: Determine the charge rate. This is usually based on the state of charge (SOC) and charging rate.

Step 2: Connect the charger to the battery, but make sure that the charger isn’t plugged in yet.

Step 3: Set the charging rate. The initial charge rate should be about 35A for 30 minutes to kickstart the charging process.

Keep in mind that charging a battery too fast can increase its temperature at a rapid rate, warping the plates in the process.

Note: Never charge or jump-start a frozen battery. A car battery can freeze up in its discharged state because the electrolyte turns into water.

A frozen battery often bulges at the sides because of water expansion. As a result, the gas pockets in the battery can explode.

Reconnecting the Battery

Once you’ve recharged or gotten a replacement battery, here’s how you can reconnect it: 

1. Place the battery on the battery tray. The battery must be level. 
2. Reinstall the battery.
3. Ensure the bolts are tight and the battery isn’t loose to prevent vibrations and displacement. 
4. Reconnect the red positive battery cable to the battery’s positive terminal. Then, connect the negative black battery cable to the battery’s negative terminal. 
5. Secure the battery’s fasteners on the battery posts. Make sure they’re tight.
6. Test the battery by starting your vehicle, turning on your headlights, and activating electronics like the radio and horn.

Battery Maintenance Guide

Most new car batteries are made with a maintenance-free design in mind. Still, it pays to keep an eye out for your battery’s condition to avoid unwanted repairs down the road.

Battery maintenance includes a thorough inspection of the electrolyte level. If the electrolyte level is low, most manufacturers recommend adding a bit of distilled water.

Proper battery maintenance also involves making sure that the battery terminals are free from corrosion, the battery case is clean, and the hold-downs are secured.

Check for loose or corroded connections at the battery terminals or the ground connector on the engine block.

If you have loose or corroded connectors, clean them using a tablespoon of baking soda mixed with a liter of water. Brush the mixture onto the battery and housing to neutralize the acid.

Then, you can proceed with cleaning the connections and washing the area with water.

Also, make sure that the battery hold-downs are secured enough to prevent the battery from moving, but not tight enough to cause the case to crack.

Where to Get a New Battery for Your Car

You can try to extend the service life of your car’s battery all you want, but there will come a time when you’ll need to replace it with a new one.

Here at CarParts.com, we’ve made online shopping for car parts easy for drivers like you. It only takes a few clicks to find what you need and a few days before you get the part you need delivered straight to your doorstep.

Take your pick from only the best aftermarket brands when you shop from our website. All our products passed strict quality checks from industry professionals, so you’re sure to get a battery that’ll get the job done.

Start shopping by entering your vehicle’s year, make, and model into our vehicle selector. This will narrow down the catalog to compatible batteries for your daily driver. You can also use the search filters to find a battery according to your preferred brand, price range, and more.

Can’t shop online? We’ve got you covered. Call us anytime using our toll-free hotline, and our team of round-the-clock customer service professionals will be ready to assist you.

Check out our products today!